TAXONOMY 



269 



to one host or distributed between two or more hosts. An outline 

 of the life history of the wheat rust will give an idea of the peculiari- 

 ties of the group. 



The Wheat Rust (Puccinia Graminis). If we examine the wheat 

 plant just before harvest we will find on the stems and leaves 



FIG. 140. Germination of the chlamydospores of corn smut ( Ustilago zece) ; i, 

 Various stages in germination from corn 3 days after being placed in water; 2, 

 spores germinated in contact with air; 3, several days after spores were placed in 

 /*20 P er cent, acetic acid, formation of infection threads, a, Spores; b, promy- 

 celia; c, basidiospores; d, infection threads; e, detached pieces of mycelia. (After 

 Bull. 57, Univ. III. Agric. Exper. Stat., March, 1900.) 



some rust-red lines. The presence of the mycelium of the fungus in 

 the intercellular spaces of the host does not kill the host directly 

 or appear to stunt its growth, but the effect of the parasite on the 

 host is seen when the grains mature. The grains are small and 

 mushy, due to the fact that the nutrition of the host had been dis- 

 turbed and the formation of starch in the grains inhibited, The 



